Traditional products for the treatment or prevention of insect or parasite infestation of animals include shampoo treatments, insecticidal collars, orally ingested treatments, compositions designed to treat an animal's environment, spot-on treatments, and the like. Different treatment forms offer unique benefits and drawbacks; however, the majority offer substantial disadvantages. For instance, shampoo treatments require that the treatment be applied over the entire surface of the animal and subsequently rinsed off, which is typically unpleasant for both the animal and the owner and only provides a short-term, transient treatment. Insecticidal collars require the animal to physically wear the collar for a period of time often lasting several months, which is uncomfortable and burdensome to the animal. Additionally, treatments administered orally tend to increase the possibility of side effects and are more difficult to administer to the animal. Alternatively, treatment of the animal's surroundings and habitat is often undesirable due to the fact that the treatment may cause discoloration of furniture, carpet, bedding, etc., and may also produce unpleasant odors. Thus, it is desirable to have a spot-on treatment that can be applied to the animal in smaller portions, while maintaining treatment efficacy across the entire body surface of the animal.
Spot-on compositions have been previously developed to incorporate a multitude of pesticide agents. Common agents include arylpyrazole derivatives, insect growth regulators, pyrethroids, nodulisporic acid derivatives, neonicotinoids, formamides, avermectins, and the like. All of the compounds listed herein have different mechanisms of action, and accordingly treat and prevent infestation in different manners. Consequently, the various compounds also have a variety of different adverse effects associated with treatment. The various agents may be combined in a variety of concentrations. Generally, higher concentrations of the active components result in higher pest kill rates, and more successful treatments; however, the use of higher concentrations of the active components are more expensive to make and result in a greater likelihood that the animal will suffer adverse effects from treatment. Higher concentrations of the active components are also less stable in preparations, present difficulties in solubilizing the actives, and present reduced storage stability, as the active components can precipitate or crystallize out of solution during prolonged storage at low temperature conditions and during repeated freeze-thaw cycles commonly experienced during shipping and storage. Most, if not all, currently available pesticidal formulations containing high concentrations of active compounds rely on steric repulsion to stabilize the formulation. Steric repulsion is typically achieved through the use of polymers, such as polyvinyl alcohol or polyvinylpyrrolidone (PVP), which may be further combined with surfactants to coat the surface of colloids and prevent the actives from crystallizing. However, polymers have proven to be ineffective when combined with certain solvents needed to solubilize particular active pesticide compounds.
Therefore, it would be desirable to have a spot-on pesticide composition with improved storage stability compared to commercially available products even when the compositions comprise high concentrations of active pesticides. In addition, it is an object of the invention to provide a novel solvent system that improves stability of pesticidal compositions, solubilizes the active compounds, and inhibits crystallization of the actives when exposed to freeze/thaw conditions.